Reduction of tank corrosion



March 13, 1962 w. 1.. MILLER REDUCTION OF TANK CORROSION Filed June 16,1959 IN V EN TOR. M44 727? L Mauve arena thee 3,fi24,6l7 Patented Mar.13, 1962 3,024,617 REDUCTION OF TANK CORROSION Walter L. Miller, 160Hendrickson Ave, Lynbrook, FLY. Filed June 16, 1959, Ser. No. 820,831 17Claims. (Ci. 6254) (Granted under Title 35, US. Code (1952), see. 266)The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This invention relates to the reduction in the corrosion of walls oflarge tanks that are used to store or convey vaporizable cargo liquidswhich are immiscible with water.

Various procedures have been used heretofore to reduce corrosion of thewalls of large tanks, particularly in tanker ships, by drying air or gasand then circulating it through the air spaces of the cargo tanks. Thisrequires means for cleaning and drying the air or gas, and elaboratecirculating equipment. Very large volumes of air or gas must becirculated in order to remove moisture from initially wet walls, bottomsand seepage. Another attempt to solve this problem was to place dryingagents in closed spaces, but such agents must, at frequent intervals,either be replaced or regenerated. Drying agents are impractical inlarge spaces which must be used in carrying liquid cargos.

Objects of the invention are to provide an improved means and method forreducing the corrosion of walls of large tanks, which require no movingparts or equipment except to compress, cool and circulate the coolingmedium or refrigerant, which employs small diameter piping, which causesno contamination of cargo and no loss of volatile portions of the cargoliquid, which employs no chemical desiccants, which has a minimum ofloss of volatiles through conventional breather valves on tanks, whichreduces corrosion of tank walls beyond that caused by a reduction inhumidity by virtue of lowered tank temperatures, which is independent ofthe nature of the air or gas in the tank and reduces the corrosionthrough lowered humidity and temperature, and which is simple, andpractical, uses compact and relatively inexpensive apparatus, andrequires little servicing attention.

Other objects and advantages will be apparent from the followingdescription of one example of the invention and the novel features willbe particularly pointed out hereinafter in connection with the appendedclaims.

In the accompanying schematic drawing a sectional elevation of the upperpart of a cargo tank is illustrated, having applied thereto apparatusfor reducing the corrosion of the tank walls in accordance with thisinvention.

In the illustrated embodiment of apparatus useful for reducing corrosionin accordance with this invention, the cargo tank includes side walls 1and a top wall 2. This tank, in this example, is used to store andtransport a liquid lighter than water, such as a petroleum product andsuch tanks are seldom, if ever fully filled with the cargo liquid, andhave an air or vapor space at the top to allow for expansion of theliquid during temperature changes in the cargo liquid. In this air spaceat the top of each such cargo tank, and above the maximum expectedliquid level therein, a heat exchange element or unit 3 is disposed andmounted in any suitable manner. A refrigeration unit 4 operated by amotor 5 or other source of power is disposed exteriorly of the tank andconnected by pipes 6 to the ends of the heat exchange unit 3 so as topass through the unit 3 a suitable cooling medium. One of the pipes 6may have a motor operated pump or circulator 7 therein to circulate thecooling medium through element 3. It is not necessary that this coolingmedium be cooled below the freezing temperature of water, but it shouldbe cooled by the unit 4 to a temperature which will cause the heatexchange element 3 to cool the adjacent air or ambient vapors to about50 F. or lower. Frosting of the element 3 may be prevented by usinglarge cooling surfaces of element 3 at temperatures above freezingtemperatures, or by periodic defrosting of the element 3 whenever it isnecessary to use temperatures below freezin for eflicient cooling.

A tray 8 is disposed in the tank 1 beneath the heat exchange element 3to catch ambient vapors condensed by the element 3 and droppingtherefrom. The element 3 is exposed for contact by ambient vapors in theupper part of the tank, and the condensation of some of the ambientvapors will set up convection currents that cause more ambient vapors tocome in contact with the element 3 and be condensed thereby. A sump 0rcasing 9 is disposed in the tank and supported in the upper air spacethereof in any suitable manner such as by suspending it from the topwall 2 of the tank.

A pipe 10 connects the tray 8 to the sump 9' and drains into the sump bygravity the condensation from element 3 that is collected in tray 8. Thesump has an overflow passage or pipe 11 in its side wall intermediate ofits top and bottom edges, and no higher than the opening of pipe 10 atthe tray. The condensed vapors of water and of the cargo liquid storedin the tank, when deposited in the sump will stratify into layers,according to the specific gravities of the water and stored cargoliquid. Th liquid of higher specific gravity will settle to the bottom,and the lighter liquid will float on the lower layer of liquid. In thecase of petroleum products the products will float as a layer on thewater layer.

In the drawing, a possible upper level of a layer of the water in thesump is shown by dot and dash line A, and a possible upper level of alayer of gasoline floating on the water layer in the sump is shown bythe dot and dash line B. When the level B rises to or beyond theoverflow 11, the gasoline or condensed cargo liquid forming the upperlayer will pass out of the sump through the overflow 11 and be returnedto the body of cargo liquid in the tank.

Before the level A of water reaches the overflow 11, it should bewithdrawn and isolated as necessary to prevent level A from reaching theoverflow. For this purpose, a pipe 12 may depend into the sump to nearthe bottom thereof, and at its upper end have means to withdraw thewater from the sump. For example a pump 13, operated by a motor 14 maybe disposed outside of tank 1, such as above the tank top 2, andconnected at its intake side to the upper end of pipe 12, The motor isoperated, as needed, through operation of switch 15, to keep the waterlevel below the overflow.

The sump is preferably placed within the top zone of the tank interior,but it can, if desired, be placed at the bottom of or even outside ofthe tank. The sump may advantageously have an aperture 9a near its top.This will permit any cargo liquid which enters the sump throughcondensation or splashing to be returned to the cargo space by overflow11. In order that one may know when water level A closely approaches theoverflow, making advisable the removal of some of the water from thesump, a tube 16 extends from near the bottom of the sump upwardlythrough the top 2 of the tank. Within this tube 16 is confined a float17 which floats in water but sinks in the lighter cargo liquid such asgasoline. This float has a rod-like stem 18 extending upwardly in thetube 16 and above its top, which stem by its position or extent ofprojection above the upper end of tube 16, indicates the level of waterin the sump.

It is important that the element 3 and tray 8 be located within and atthe top of the vapor space inside the tank and above the maximumexpected liquid level therein. This makes it possible to have acontinuous condensing action on the mixed vapors of water and the cargoliquid, accompanied by separation in the sump of the condensed vapors ofthe water and the cargo liquid with isolation and removal of thecondensed water. This action is independent of the vapor pressure withinthe vapor space of the tank, and there is a continuous cycling of theambient vapors within the vapor space past and under the condensinginfluence of the cooling element. The cooled dry air and vapor at theelement 3 is heavier than the warmer humid air and vapor at the liquidsurface, and this causes a continuous movement downwardly of the air andvapor past the element 3, during which the water and cargo liquid vaporsare condensed and other air and vapor replaces the downwardly moving airand vapor. The convection currents thus established are fortified, whenthe ship having the cargo tanks, is moving, through movement of thecargo liquid in the tank.

While this method and apparatus are particularly useful in tankscarrying a vaporizable cargo liquid, they are also very useful in tankscarrying non-vaporizable cargo liquids, in which latter case the coil 3will condense water vapors in the air that is present above the storedliquid and thus reduce possible corrosion of the tank walls that mightbe caused by the presence of water vapors in the tank above the liquidcargo. While it is advantageous to have the sump 9 within the upper partof the tank, it can be placed elsewhere in the tank or even outside ofit. The sump is also useful in separating the condensed water vaporsfrom any of the cargo liquid whether condensed vapors of the cargoliquid or just spray from the cargo liquid, that may get into the tray 8along with condensed water and other vapors.

It will be understood that various changes in the details, materials andarrangements of parts, which have been herein described and illustratedin order to explain the nature of the invention, may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the appended claims.

I claim:

1. Apparatus for reducing corrosion in a closed ships cargo storage tankunder atmospheric pressure and containing a stored liquid immisciblewith, and of different specific gravity from, water, which comprises thecombination with said tank of a heat exchange element supported in thefull open space in the main body of said tank above the maximum expectedliquid level therein, means connected to said element and supplyingthereto a cooling medium and forming therewith a complete refrigeratingunit independent of and separate from said tank and said storage liquid,a collector member in said tank disposed beneath said element, alsoabove said maximum expected liquid level, and having an upwardly openface at least coextensive in area with the overall horizontal areaoccupied by said element, for collecting condensations by said elementof ambient vapors in the atmosphere above said maximum level, saidelement being unenclosed and fully exposed for continuous contacttherewith of said ambient vapors, a sump disposed with a portion belowthe level of said collector member, means for draining condensed vaporsand any spray of the stored liquid created by motion of the tank andcollected by said member into said sump where they may stratify andseparate the condensed water from said tored liquid, means for returningthe condensed said stored liquid from said sump to said stored liquid insaid tank, and means for removing excess water from said sump.

2. Apparatus for resisting corrosion in a closed tank containing avaporizable liquid lighter than and immiscible with Water, whichcomprises the combination with said tank of a heat exchange elementsupported in the full open space in the main body of said tank above themaximum expected level therein of said liquid, means outside of saidtank connected to said element and sup- ,4 plying thereto a coolingmedium and forming therewith a complete refrigerating unit independentof and separate from said tank and said storage liquid, a collector trayin said tank and disposed beneath said element and also above saidmaximum expected level, and opening upwardly beneath all of the overallhorizontal area occupied by said element for receiving condensations bysaid element of ambient vapors in the space of said tank above saidmaximum level, said element being unenclosed and fully exposed forcontinuous contact therewith of said ambient vapors, a sump, means forconducting into said sump any condensed vapors collecting in said tray,said sump having an outlet for removal of said vaporizable liquid whichseparates by stratification from the water in said sump, and means forremoving condensed water vapors from the lower part of said sump.

3. Apparatus for application to a closed tank containing a liquidimmiscible with water, for reducing corrosion of interior tank walls byambient water vapor in the tank, which comprises a heat exchange elementto be supported in the interior of the full open space in the main bodyof said tank above the maximum expected level of said liquid therein andfully exposed for contact therewith continuously by ambient vapors inthe tank to condense them, means forming with said element a completerefrigeration system independent of and separate from said tank and itscontents, and delivering a cooling medium to said element, means havinga fully open upper face for collecting condensations by said element ofambient vapors in the space of said tank above said maximum liquid levela sump disposed to receive said condensations and in which thecondensations may stratify into separate layers of water and saidliquid, said sump having an outlet through which any of said storedliquid therein may be removed and returned back into said tank, andmeans connected to the interior of said sump for removing therefromcondensed waters vapors from the layer of water as necessary.

4. Apparatus for reducing corrosion in a relatively large closed storagetank containing liquids lighter than and immisicible with water, whichcomprises the combination with such tank of a heat interchange unitsupported in the top space in the main body of said tank above themaximum expected liquid level therein, means outside of said tank forsupplying a cooling medium continuously to said unit and formingtherewith a complete refrigerating unit independent of and separate fromsaid tank and said storage liquid, a tray with an open upper facedisposed within said tank beneath said unit, also disposed above themaximum expected liquid level in the tank, for receiving and collectingvapors condensed by said unit, said unit being unenclosed and fullyexposed for continuous, direct contact therewith of ambient vapors inthe top portion of said tank, a sump having a chamber separate from saidtank, means connecting said tray with said sump for conducting condensedvapors from said tray to said sump, means connected to the lower part ofsaid sump for removing water therefrom, means for discharging into saidtank liquids from a selected zone of said sump, whereby when the Waterand condensed vapors from said stored liquid and splash from the liquidseparate into separate layers, the water may be removed before itreaches said discharging means and the other condensed vapors and liquidcan return to the unvaporized liquid in said tank.

5. The apparatus according to claim 1, wherein said means for supplyingsaid cooling medium to said exchange element is disposed outside of theliquid storage space of said tank.

6. The apparatus according to claim 1, wherein said sump is disposed ata level above said maximum expected level, and has a gravity drain fromthe part thereof occupied by the stratified condensed vapors of thestored liquid into said tank below said sump.

7. The apparatus according to claim 2, wherein said sump is locatedwithin said tank and above said maximum level.

8. The apparatus according to claim 1, and means connected to said sumpand operable to indicate the level of water in said sump.

9. The apparatus according to claim 3, and means connected to said sumpand operable to indicate exteriorly of the tank and sump the position ofthe stratified division between the water and said liquid in the sump.

10. Apparatus for reducing corrosion in a closed tank containing astored liquid which i immiscible with water and incompletely fillingsaid tank which comprises the combination with such tank of meansdisposed in the open space in the upper part of the main body of saidtank and unenclosed and fully exposed for continuous contact with allambient vapors in the upper part of the tank, for condensing out thecondensible part of ambient vapors from the air in the space between themaximum liquid level in said tank and the top of the tank, means havingan upwardly opening collector also in said space in the upper part ofsaid tank and immediately below said condensing means disposed toreceive the condensed vapors, means connected to said receiving meansand operable to separate from the col lected condensation the condensedwater, means by which the separated water may be removed and discarded,and means by which the balance of the condensed vapors may be returnedto the tank.

11. The method of reducing corrosion in a closed liquid storage tankcontaining a liquid immiscible with water, and having a maximum levelbelow the top of said tank, which comprises continuously condensingwithin the tank, in the space thereof above the liquid level therein,the ambient vapors in the space between said maximum liquid level andthe top of said tank, continuously collecting the condensed vaporswithin the tank and causing them to stratify into separate layers ofwater and said liquid, removing said layer of said liquid and returningit to the body of said liquid in said tank, and removing said water ofsaid water layer sufficiently to prevent its return to said body ofliquid in said tank with said removed layer of said liquid.

12. The method of reducing corrosion in a closed ships cargo storagetank containing a liquid lighter than and immiscible with water, andhaving a maximum level below the top of said tank, which comprisescontinuously condensing within the tank in the space above the liquidlevel therein, the ambient condensible vapors in the space between saidmaximum liquid level and the top of said tank, causing the condensedvapors and any splash of the said liquid that may be caused by themotion of the ship, and becoming mixed with the condensed vapors tostratify into separate layers of water and said liquid, draining off andisolating the stratified layer of condensed water, and returning thelayer of condensed liquid to said tank.

13. The method of reducing corrosion in a closed tank under variableatmospheric pressure containing a stored liquid immiscible with water,and having a maximum level below the top of the tank, comprisingcontinuously condensing out within the tank in the space above theliquid level therein, the condensible part of ambient vapors from theair in the tank space between said maximum level and the top of saidtank, separating out and discarding the water from said condensedvapors, and returning the balance of the condensed vapors to the tankinterior.

14. Apparatus for reducing corrosion in closed, ships cargo tank underatmospheric pressure that is used to store a liquid that is immisciblewith and of different specific gravity from water, and vapon'zes to someextent under atmospheric pressure, which comprises the combination withsaid tank of a heat exchange element supported in the top portion of themain body of said tank above the maximum expected level of stored liquidtherein and exposed to continuous direct contact with ambient vapors insaid top portion for heat exchange therewith, means for supplying acooling fluid located exteriorly of said tank and connected to saidelement for circulating said cooling fluid through said element andforming with the latter a complete refrigeration unit independent of andseparate from said tank and said stored liquid, an upwardly opening traydisposed in said tank immediately below said element and also above thesaid maximum expected level of stored liquid in said tank, and of a sizeto collect substantially all of the ambient air and vapors condensed bysaid element and any spray and splash therein of the stored liquid dueto motion of the tank, -a sump connected to said tray to receive fromthe tray any liquid collecting in said tray and in which sump thecondensed vapors of said stored liquid and water vapor may stratify andseparate into superposed layers, a level indicator connected to saidsump for indicating the upper level of one of the said stratifiedlayers, means connected to said sump by which a desired part of thelayer of condensed vapors of the stored liquid in said sump may beprogressively removed from the sump and returned to said tank, and meansalso connected to said sump for removing to the exterior of said tankand discarding any part of the condensed water layer.

15. The apparatus according to claim 14, wherein said sump is located inthe upper part of said tank also above said maximum expected level ofstored liquid, and the means connected to said sump enabling removal ofcondensed vapors of the stored liquid includes a gravity drain into saidtank for such condensed vapors of the stored liquid.

16. The apparatus according to claim 14, wherein said heat exchangeelement has a closed passage therethrough for the passage of a coolingfluid therethrough, and an outer exposed surface in the space of saidtank above said maximum expected level of stored liquid, whereby thecondensation of ambient vapors in the tank is continuous.

17. The method of reducing corrosion in a storage tank for volatileliquids that are immiscible with water and which has a vapor space inthe upper part thereof above the maximum expected liquid level therein,which comprises continuously exposing all ambient vapors in said spacewhile confined in said space to an exposed and uncovered cooled surfaceat a temperature that condenses from such ambient vapors the vapors ofsaid stored liquid and water vapors, continuously collecting all of saidcondensed vapors in said space, and separating the water condensationfrom the condensation of the stored liquid, continuously returning thecondensation of the stored liquid to said tank, and discarding the watercondensation.

References Cited in the file of this patent UNITED STATES PATENTS2,059,942 Gibson Nov. 3, 1936 2,321,964 Zieber June 15, 1943 2,344,765Dana et al Mar. 21, 1944 2,379,215 Brinkmann June 26, 1945 2,449,688Brinkoeter Sept. 21, 1948 2,577,598 Zwickl Dec. 4, 1951

